Does Chromoly have a 'life?'

[leec]

Talking last night about Chassis materials, someone said to me Chromoly tubing has a useable life (9 years)
Does that sound correct and would a tube chassis only last for 9 years then would need replacing or am I talking absolute rubbish?

Lee

[Chris bugster]

From what I learned talking to chassis builders, it's not so much the time but the use that counts. For example, a Top Fuel dragster will need a new chassis after 20 passes, but a VW Bug chassis will typically last 500 passes.Of course, even with Beetles, a tube frame Bug with 100hp and 6 inch slicks will live longer than a 1000hp turbo car with 8.5 slicks. All this depends on how they are run so it's difficult to estimate. Stress meters etc would be ideal.

[MeXX]

Talking last night about Chassis materials, someone said to me Chromoly tubing has a useable life (9 years)
Does that sound correct and would a tube chassis only last for 9 years then would need replacing or am I talking absolute rubbish?

Lee

If a Chromoly chassis dies after 9 years where is the cemetery ?

MeXX

[dannyboy]

how much life does a big arsed wheelie take off a car

[stealth67vw]

Talking last night about Chassis materials, someone said to me Chromoly tubing has a useable life (9 years)
Does that sound correct and would a tube chassis only last for 9 years then would need replacing or am I talking absolute rubbish?

Lee

If a Chromoly chassis dies after 9 years where is the cemetery ?

MeXX

The US guys sell them to Europeans     

[Jim Smith]

That depends on what you are wanting the moly to do??? If you are using it to allow a structure to flex, then yes it does have a life in so much as the amount of flex you designed into the structure from the outset will change with use. However from a strength point of view in a stiff chassis, you should have nothing to worry about. After all, you can still get a 10 year+ moly chassis tagged. A good example is a pair of moly wheelie bars that will spring just how you want them to from new, but after much use will start to behave very differently.

[leec]

That depends on what you are wanting the moly to do??? If you are using it to allow a structure to flex, then yes it does have a life in so much as the amount of flex you designed into the structure from the outset will change with use. However from a strength point of view in a stiff chassis, you should have nothing to worry about. After all, you can still get a 10 year+ moly chassis tagged. A good example is a pair of moly wheelie bars that will spring just how you want them to from new, but after much use will start to behave very differently.

Thanks Jim,
A perfect answer to my question. It's amazing how many myths get created

Lee

[Bernard Newbury]

That depends on what you are wanting the moly to do??? If you are using it to allow a structure to flex, then yes it does have a life in so much as the amount of flex you designed into the structure from the outset will change with use. However from a strength point of view in a stiff chassis, you should have nothing to worry about. After all, you can still get a 10 year+ moly chassis tagged. A good example is a pair of moly wheelie bars that will spring just how you want them to from new, but after much use will start to behave very differently.

Surely that would apply to any metal used in a built in flex situation. ?

[MeXX]

Hi

To understand why a CrMo part may have a shorter live than a similar mild steel part you have to understand the difference of this two materials.
1. CrMo has nearly double the strength than mild steel. That's good.
2. The higher the strength gets the more the steel tends to be brittle. That's bad.  
3. What is even more importand is the elongation which the percentage a steel can be stretched before it breaks.

As you can see CrMo used in aircraft and helicopters CrMo is the better material for chassis and if it is designed correctly there should be never a problem with it's life.
If it's designed "on the edge" you have to take care, but it's not the time it's the load and the cycles that shortens the life.
As Top Fuel cars have no suspension and the chassis has to flex to do this job it is definitely designed on the edge, it also has to take enormous loads from the engine an when tire shake occurs.

More than often failures are caused by the design than by the strength (wheelie bars).

check out this video to understand what tireshake does and how a wheelie bar has do be designed to flex.

<a href="http://www.youtube.com/v/mfJejgODr3E" target="_blank">http://www.youtube.com/v/mfJejgODr3E</a>


MeXX

[henk]

they make motorbike frame out of chromoly tubing and there is no lifespan on them.
off course they don't get that much abuse as a top feul.

henk!!!